operator==,!=(std::function) - cppreference.com (original) (raw)
| Defined in header | ||
|---|---|---|
| template< class R, class... ArgTypes > bool operator==( const std::function<R(ArgTypes...)>& f, std::nullptr_t ) noexcept; | (1) | (since C++11) |
| template< class R, class... ArgTypes > bool operator==( std::nullptr_t, const std::function<R(ArgTypes...)>& f ) noexcept; | (2) | (since C++11) (until C++20) |
| template< class R, class... ArgTypes > bool operator!=( const std::function<R(ArgTypes...)>& f, std::nullptr_t ) noexcept; | (3) | (since C++11) (until C++20) |
| template< class R, class... ArgTypes > bool operator!=( std::nullptr_t, const std::function<R(ArgTypes...)>& f ) noexcept; | (4) | (since C++11) (until C++20) |
Compares a std::function with a null pointer. Empty functions (that is, functions without a callable target) compare equal, non-empty functions compare non-equal.
| The != operator is synthesized from operator==. | (since C++20) |
|---|
[edit] Parameters
| f | - | std::function to compare |
|---|
[edit] Return value
1,2) !f
3,4) (bool) f
[edit] Example
#include #include using SomeVoidFunc = std::function<void(int)>; class C { public: C(SomeVoidFunc void_func = nullptr) : void_func_(void_func) { if (void_func_ == nullptr) // specialized compare with nullptr void_func_ = std::bind(&C::default_func, this, std::placeholders::1); void_func(7); } void default_func(int i) { std::cout << i << '\n'; }; private: SomeVoidFunc void_func_; }; void user_func(int i) { std::cout << (i + 1) << '\n'; } int main() { C c1; C c2(user_func); }
Output:
[edit] See also
| | compares a std::move_only_function with nullptr (function) [edit] | | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |